Fluorescence microscopes commonly utilize multiple polychroic mirrors attached to a polychroic changer in order to excite a number of different fluorescent emission channels that can be separately imaged. However, aligning the system for multiple polychroic mirrors remains a challenge. In particular, replacing one polychroic mirror located in an excitation beam path with another is difficult to achieve with a high degree of alignment precision and repeatability. In addition, co-alignment of the multiple polychroic mirrors is very difficult to achieve.
Prior approaches include using polychroic mirrors that are mounted to angled surfaces of turret systems. Each angled position of the turret has a different polychroic mirror. A conventional turret has repeatability problems because there are typically multiple parts that index the polychroic mirror position with respect to one another as well as with high respect to the microscope. This makes it nearly impossible to guarantee with precision that two or more polychroic mirrors are co-aligned. It is possible to add mechanical adjustment controls to provide the necessary degrees of freedom to co-align multiple polychroic mirrors. However, these additional mechanical adjustment controls increase the costs and complexity of a microscope considerably, as well as further reducing long term alignment repeatability. For instance, adding parts associated with an adjustment mechanism to a polychroic mirror changer results in changes in positions of the optical components over time. For these reasons, fluorescent microscope manufactures and engineers continue to seek reliable systems for changing polychroic mirrors.